The present invention relates generally to a hydraulically-actuated system, and more specifically to a fluid pump having a position sensor adapted to sense actuator position.
U.S. Pat. No. 6,035,828 to Anderson et al. describes a system having a variable delivery fluid pump. In this system the pump supplies fluid to a hydraulically-actuated fuel injection system. The pump outlet supplies high pressure lubrication oil to a plurality of hydraulically-actuated fuel injectors of a diesel engine. The pump is driven directly by the engine, and pump output is varied by an electronically controlled actuator. A pressure sensor is provided in the system that monitors the actual fluid pressure within the system. An electronic control module monitors fluid pressure and a number of engine operating parameters to determine if actual fluid pressure is sufficient for current engine operating conditions. To minimize the output of emissions of the engine, precise control of fluid pressure is critical.
If actual pressure is below a predetermined desired pressure the controller calls for higher pump output. As desired pressure is reduced the pump output is reduced. Because control strategy is based on pressure data only, the controller must estimate how far to move the actuator in a given direction.
Monitoring and controlling pump output based on actual pressure typically works well, although occasions arise that reduce the effectiveness of this control method. One such example, the viscosity of lubrication oil varies due to oil temperature and condition. The variability of fluid viscosity, in turn, varies the speed that the actuator moves. Movement of the actuator directly relates to pump control.
In some cases the pump may overshoot or undershoot desired system pressure. Even very small differences in actual pressure and desired pressure can adversely impact emissions and engine efficiency.
The present invention is directed to overcoming one or more of the above identified problems.
In one aspect of the present invention a fluid actuated system is provided. The fluid actuated system includes a variable delivery pump having a piston and a high pressure conduit. An actuator having a plunger and a position sensor adapted to deliver a position signal are connected to the pump. A fluid pressure sensor is connected to the high pressure outlet and adapted to deliver a signal related to a fluid pressure. An electronic control module is adapted to receive the pressure and position signals and send a directional control signal.
In another aspect of the invention a method of controlling a fluid pump is provided. The method includes the steps of sensing the pressure fluid in a high pressure conduit, sensing the position of an actuator and delivering a position related signal and delivering a directional move signal in response to the pressure signal and the position signal.
In yet another aspect of the present invention a method of estimating the viscosity of a fluid in a hydraulically actuated system is provided. The method includes the steps of sensing a first position of a moveable device within the system, delivering a directional move signal to the moveable device and sensing a second position of the moveable device, calculating a speed of said moveable device and calculating the viscosity of the fluid.